Stanford team explores hypersonic flight theory

The possibility of hypersonic flight — offering endless potential in air and space travel but also posing numerous engineering challenges — recently became the domain of Stanford engineers. The Stanford Predictive Science Academic Alliance Program (PSAAP) received a five-year $20 million grant from the U.S. Department of Energy (DOE) to investigate the subject virtually.

The DOE awarded grants to five universities interested in researching and developing solutions to overarching problems as varied as the hypervelocity impact of metallic projectiles and the atmospheric re-entry of space capsules. The Stanford team chose to tackle the challenge of hypersonic flight, which could potentially result in speeds of up to 15 times the speed of sound.

(M.J MA/The Stanford Daily)

“We considered many applications for our predictive science program before submitting our final proposal,” said Parviz Moin M.S. ‘75 ‘78 Ph.D. ‘78, professor of mechanical engineering and PSAAP faculty director. “We finally settled with hypersonic flight as we thought it would be a project we would have fun with and enjoy working on, and it was a technological grand challenge.”

The project also allows for multidisciplinary cooperation between the Computer Science, Aeronautic and Astronautic Engineering, Mechanical Engineering and Mathematics departments, as well as Stanford’s Institute for Computational and Mathematical Engineering.

“An overarching problem like this one is the best catalyst to promote interdisciplinary research,” Moin said. “Thanks to the combined work of these departments, we have already pushed and developed new numerical techniques, physical models and computational platforms that are paving the way for predictive science.”

Stanford is at the cutting edge of research in the discipline, according to Moin, having even pioneered a new science known as uncertainty quantification.

“Uncertainty quantification allows us to assess uncertainties in our numerical solutions,” Moin explained. “We can back up our predictions with data about the error bounds.This might be the most important topic in the future of computational science.”

Moin also highlighted the impact of the DOE grant on the program’s operations.

“We have essentially been able to create a new mini national laboratory,” Moin said. “We have a large cadre of postdoctoral fellows and graduate students who interact in a way that has never been seen before. It has been a paradigm shift in the way we do research.”

The “large cadre” of faculty, postdoctoral fellows and graduate students is necessary to tackle the challenges of hypersonic flight, according to Moin.

“Nobody has been able to sustain hypersonic flight propulsion for a longer amount of time,” Moin said. “Most tests have failed, and the few who succeeded lasted for only a few seconds.”

The problem, Moin said, is that at hypersonic speed air flows into the combustion chamber of a scramjet engine at speeds up to Mach 15. The time in which the combustion has to occur is infinitesimally short, and mastering such a reaction is the main challenge of the project.

“The equations are all well-known, but they are very hard to solve,” Moin said.

The team’s extensive collaboration with the Computer Science Department, and the use of some of the world’s fastest supercomputers to model hypersonic flight, is a direct consequence of the equations’ complexity.

“We are heading towards exascale computations, with more than one quintillion flops [floating-point operations per second] and one million cores running simultaneously,” Moin said, explaining that the coding and handling of such supercomputers has required extensive Computer Science involvement.

The breakthroughs the Stanford PSAAP team has already made and anticipates making in researching hypersonic flight are likely to impact many other fields.

“We now know how to simulate very complex flow dynamics,” Moin said. “This very technology can also be applied to automobiles, wind turbines, new energy conversion technologies and in environmental science.”

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